1. Field of the Invention
The present invention relates generally to wireless communications and, in particular, to a method and apparatus for configurable selection and acquisition of a wireless communications system.
2. Description of the Related Art
A mobile device will often have access to more than one wireless communications system in its geographic region. The quality of the wireless services available to the mobile device may vary from system to system depending on the equipment used by each system, the features of the mobile device, the distance between the mobile device and local base stations, physical obstructions such as buildings and hills, and the volume of communications traffic on each system. The local wireless communications systems may also support different multiple-access wireless communications protocols such as code division multiple access (CDMA), wideband CDMA (WCDMA), Advanced Mobile Phone Service (AMPS), Global System for Mobile communications (GSM), General Packet Radio Services (GPRS) or High Data Rate (HDR) technology (e.g., 1×EV technology). In addition, the fees charged to a user of the mobile device may vary depending on the time of day, the duration of the connection with the wireless communications system and whether the mobile device is listed as a subscriber of the wireless communications system.
In operation, a conventional mobile device selects and attempts to acquire and register with at least one of the available wireless communications systems. To assist with the selection of a desirable system, the mobile device typically stores systems data that identifies the wireless communications systems that are compatible with the mobile device. In one approach, the systems data is a preferred roaming list (PRL) that includes a systems table, which stores a system identifier (SID) and a network identifier (NID) for each wireless communications system, and an acquisition table, which stores acquisition parameters including band, frequency and mode for the systems listed in the systems table.
Within the systems table, the wireless communications systems are often grouped by geographic region and sorted from the most desirable to the least desirable system in each region. The most desirable system in a particular geographic region is typically a subscriber system, but may also be a roaming system that offers the mobile device a favorable combination of low cost and high quality of service. Roaming systems offer wireless services to non-subscriber mobile devices, usually at a much higher fee than subscription services, and may be desirable when the mobile device enters a geographic region that is outside the coverage area of the mobile device's subscription service, when the subscription services are blocked or otherwise unavailable, or when the subscription services are only available at an unacceptably low level of quality. The systems table is typically maintained by the mobile device's wireless services provider through periodic downloads of updated systems data. By controlling the content of the systems table, the mobile device's wireless services provider may establish an order of priority among the listed systems that steers the system selection process towards its own systems and its partner's systems.
A conventional mobile device also includes system selection logic that defines a system selection and acquisition procedure. The system selection and acquisition procedure dictates how and when systems are selected from the systems table, which systems should be given priority, which systems should be avoided, the types of data that should be maintained for each system and other criteria that impacts the system selection order. In a common system selection and acquisition procedure, the mobile device first steps through a list of the systems that were most recently used by the mobile device, attempting to acquire and register with each system until a system acquisition and registration attempt is successful. If these systems are exhausted without a successful system acquisition, the mobile device attempts to acquire and register with one of the systems listed in the systems table, starting with the most desirable system in the current geographic region and working through to the least desirable system in the current geographic region. If these acquisition attempts are unsuccessful, the mobile device scans available frequencies in an exhaustive search for a local system.
Unlike the systems table, which may be easily modified by a wireless service provider, the system selection and acquisition logic, which controls when and how the systems are selected from the systems table, is difficult to modify. The system selection and acquisition logic of a conventional mobile device is hard-coded into the circuitry of a system determination unit. If the wireless services provider or mobile device manufacturer is not satisfied with the system selection and acquisition logic in preexisting system determination units, a proprietary system determination unit may be created. Configuring a system determination unit with unique program logic requires the generation of a corresponding software image, which must be tested and loaded into the new system determination unit. This process is expensive, hard to manage and time consuming. Further, even if desirable system selection and acquisition logic is initially selected for the mobile device, the wireless services provider may later desire to update the system selection and acquisition logic. Changing the system selection and acquisition logic will require replacing the current system determination unit with a new system determination unit that encapsulates the desired procedure, a process that is generally cost prohibitive, inconvenient to the user and, as a result, seldom performed in practice.
To accommodate the specific requirements of different mobile device manufacturers, wireless services providers and markets, there is a need in the art for an efficient and cost effective method and apparatus that allows manufacturers and wireless services providers to configure and modify the system selection and acquisition logic in a mobile device.